Electric machine.



1 F. G. LILJENROTH.

ELECTRIC MACHINE.

APPLICATION FILED MAY 20. I916.

Patented Nov. 20, 1917.

' UNITED S TES PAT NT OFFICE ,FRANs GECSRG LILJENRo'rH, 0F wris'rnnlis, SWE EN.

I LE TRIC MACHINE.

To all whomit may concern Be it known that'I, FRANs GEORGL'ILJEN- ROTH, a citizen oftheKingdomof Sweden, residing at Westeras, Sweden, have invented new and useful Improvements in Electric Machines, of which the following is a specification.

This invention relates to electric machines, particularly to such machines provided with commutator-s, and the object of the invention is to so construct such com'inutators, that an increased resistance to discharges beween the'diflt'erent bars be obtained.

The invention consists briefly in compos-' tudinal recesses located near to the limit surfaces of the insulating layers and extending in radial and axial directions.

In the accompanying drawing Figure 1 is a fragmentary sectional view of a commutator constructed in the usual manner. Figs.

2 and 3 are fragmentary sectional views of for consequence, that disruptive discharges in the air field 3 situated close to the layer 2 take place at a tension lowerthan that required under general circumstances for discharges through an air field of the same width as 3.

In order to prevent this inconvenience and to obtainan increased safety from discharges without increasing the thickness of the insulating layers, the lateral surfaces of the commutator bars are provided with recesses l forming lateral grooves extending parallel to the axis of the commutator placed at the outer limit surfaces or ends of the insulating layer in radial direction. By suitably sizing the recesses 4 it is obtained, that the discharge voltage above the insulating layer'2 becomes at least equal to the discharge voltage of the air field 3. These recesses or grooves 4 are cut into one side, Fig. 2, or both sides, Fig. 3, of each section and their edges nearest the axis of the commutator are slightly below the outer peripheral edges of the insulating layers 2,

which edges remain below the surface of the Snecificat ion of Letters Patent. Patented '7, Application filed l lay2 0, 1916. Serial No. 99,003.

commutator. In this manner the spacesbetween the sections at the surface of the 'comsurface of the commutator into which the outer edge of the intervening insulating layer 2 projects. ,Thisouteredge is below the surface of the commutator, so as not to be contacted by a brush trailing on the commutator, and is in alinement with a narrow air gap 6, of normal size, but below it. In other words, the grooves of adjacent segments are symmetrical with respect to the edge of the insulation 2. Corresponding recesses 5 may also be effected at the inner limit surfaces of the insulating layer as well as at the end surfaces in axial direction, as

is shown in Fig. 4.

Said recesses may be located at one side only of the insulating layer, as in Fig. 2, or at both sides thereof, as in Fig. 3.

In Fig. 2 the inner, smaller ends of the commutator sections are beveled to form a V-shaped gap, as shown at 5. The bevel is made on the same side of the section as the groove 4..

In Fig. 3 these grooves are formed on the inner ends of'the commutator segments by cutting the edges away to make them thinner, as by cutting a rabbet along opposite edges of each segment, and when assembled form pockets or gaps 5 into which the inner edges of the insulating layers pro j ect. Here also the rabbets of adjacent commutator segments are symmetrical with respect to the intervening insulation 2, as shown.

The presence of the insulating layers 2, Fig. 1, of material having a higher dielectric constant than air, produces disruptive discharges in the air field at 3 close to the layer 2, and at a tension lower than that required under general circumstances for discharges through an air field of the same without having it of such large tangential width as to cause the brushes to vibrate. This I have done by the structures illustrated in Figs. 2 and 3, where the narrow air gap 6 is sufficiently small to prevent the vibration of the brushes, while at the groove A it is 'sufiiciently wide to adequately weaken the electrical field.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is: A v

1. A commutator comprising a. plurality of metallic bars and insulating layers therebetween, said metallic bars having at their edges recesses forming grooves along the edge, the one lateral wall of each groove consisting of the portion of insulating layer adjacent to said edge, said insulating layer terminating inside the face of the commutator.

A commutator comprising a plurality of metallic bars and insulating layers therebetween, said metallic bars having at their peripheral edges undercut recesses forming grooves with ribs along the edge extending beyond the end of the insulation layers, the one lateral wall of each groove being formed by the adjacent insulating layer which tersurface of the commutator wider than and communicating with said air gaps into which said layers prO ec't.

Intestimony whereof I have signed my name.

FRANS GEORG LILJENROTH.

Copies of this patent may be obtained for five cents each, by-addressing the Commissioner of Patents, Washington, D. 0. 

